It is now well recognized in a variety of industries that core samples from well bores provide useful and sometimes invaluable information. Data regarding subsurface geological formations are of recognized value in drilling for petroleum and gas, mineral exploration, in the construction field, in quarrying operations, and in many other similar fields. In the petroleum and gas drilling field it is often difficult to secure proper or any cores from certain types of formations. For example, coring in soft formations, unconsolidated formations, conglomerates or badly fractured rock often results in loss of the core from the washing action of circulated drilling fluid, or in crumbling or other disturbance to the core. As a result, the recovered core is so badly damaged that standard tests for permeability, porosity and other parameters cannot be performed. In addition, cores that are recovered are very often disturbed even more in the attempt to remove them from the core barrel. In other instances, when the core has jammed within the core barrel the entire drill string must be brought out of the hole to remove the jammed core from the core barrel so that coring can resume. In addition, jamming often results in significant amounts of core being ground up under the jammed barrel and not recovered.
In the case of unconsolidated formations, it is known from U.S. Pat. No. 2,927,775 to use a rubber or equivalent elastic sleeve which grips the core as the core is cut. Also disclosed therein is a woven metal core sleeve. An elastomeric or fabric sleeve operates well for unconsolidated cores, but where the material being cored is fractured rock such as Monterey Shale and Chert, which is comprised of hard and very hard rocks, the alternation of consolidated bands with highly fractured unconsolidated sections not only limits the length of the core samples, but provides samples with very sharp edges and crushed granules and pebbles. The prior art elastomeric or fabric core sleeves do not operate well with this type of material.
A variation of the core sleeve is described in U.S. Pat. No. 3,511,324 which describes a finely meshed knitted fabric such as nylon and the like. However, in the structure described in this particular patent, the diameter of the core sleeve is not reduced and no resistance against a transverse deformation of the sample is provided. Moreover, the system described in this patent does not provide any constriction of the sleeve on exertion of a tensile load.
U.S. Pat. No. 4,156,469 also relates to a resilient sleeve which is bunched into a holder, the principal purpose of which is to reduce the coefficient of friction rather than the normal force of friction.
U.S. Pat. No. 3,363,705, like U.S. Pat. No. 3,511,324 previously discussed, does not grip or lift the core, although there is described therein a core-receiving sampling sleeve which is generally tubular in configuration and fabricated from nylon mesh.
U.S. Pat. No. 3,012,622, assigned to the present assignee, also describes a rubberlike coring retaining sleeve for retrieving a core from a bore hole. Again, equipment of the type described in this patent has operated successfully with certain soft unconsolidated formations, but provides somewhat poorer performance in the case of hard, abrasive rock such as conglomerates, or badly fractured rock.
Other patents which relate to core sleeves include U.S. Pat. No. 3,804,184 and those mentioned in the text of this application.
The coring devices and core sleeves described in the above-identified patent operates satisfactorily under many circumstances, but where the formation is comprised of hard, broken and fragmented rock, the core often jams within the coring device. Core jamming is caused by the friction produced between the core and the inner barrel of the coring device within which the core is located. The friction which tends to produce jamming is the product of two factors, one being the force pushing the materials together, and referred to as the "normal force" and the other being the "coefficient of friction" which depends upon the types of materials being pushed together and any lubricating fluid between them. Broken or fractured pieces of the core act like a wedge inside surface of the inner tube. The "normal force" is created by the angle of fracture and the force required to push the core upward to insert the core into the barrel. Eventually, this force exceeds the strength of the core or exceeds the drill string weight. In such an instance, the new core is crushed in the throat of the bit or the core jams, and drilling stops because of a lack of weight on the cutters of the bit.
In some of the prior patents previously identified, attempts have been made at reducing the "coefficient of friction" between the core and the inner tube as an attempted means to reduce jamming. In the main, such attempts have been ineffective because the "coefficient of friction" cannot be reduced to zero. Accordingly, with a doubling of forces with each fracture, jamming is postponed but not eliminated.
It has also been noted with respect to some coring devices of the prior art that the core catcher is mounted so that it is carried by and rotates with the bit. This may cause the coring device to disintegrate or grind up highly fractured core, thereby tending to increase jamming in the bit throat and catcher areas. It has also been noted with respect to the prior art devices that ground-up material sometimes enters between a gap which is normally present between the core catcher and the associated core shoe, thus tending to cause core jams in the region between the inner tube and the core catcher.
Accordingly, it is an object of the present invention to provide a unique coring device incorporating a unique core sleeve which grips the core tightly and eliminates friction by reducing the "normal force" rather than the "coefficient of friction" and wherein a weight is used to maintain the sleeve in compression.
Another object of this invention is to provide an improved coring apparatus including a unique woven wire mesh tube which lifts the core and prevents the fracture planes of the core from sliding and acting like a wedge, thereby substantially eliminating core jams, especially with highly fractured formations, thereby insuring relatively high core recovery and wherein the core sleeve is maintained in compression by a weight which insures proper movement of the sleeve in use.
It is also an object of the present invention to provide an improved coring apparatus which includes an approved wire metal core sleeve which insures relatively high core recovery, especially when used in formations which are highly fractured, hard formations and wherein an improved system is used to maintain the sleeve in compression until tensile forces are applied thereto.
Still another object of the present invention is to provide an improved coring device which includes a unique wire core sleeve which is maintained in a compressed condition around the inner core barrel by a weight which bears against the end of the sleeve, the sleeve being fed around the lower end of the inner core barrel, wherein tension is applied to the core sleeve in the inner barrel to compress the sleeve around the core to keep the core together, and to prevent the core from touching the inside of the wall.
A further object of this invention is to provide an improved coring device including a unique core sleeve and wherein a weight cooperates with the core sleeve to maintain the latter in compressed condition between the inner core barrel and the intermediate tube, thereby permitting the core sleeve to be fed easily around the lower end of the inner core barrel.
Still a further object of the present invention is the provision of an improved coring apparatus in which a core sleeve is positioned between the inner barrel and the intermediate tube, a weight being located above the sleeve and between the tube and barrel, and wherein the intermediate tube is connected to a non-rotating inner barrel, with a core catcher connected to the intermediate tube below the core sleeve, thereby eliminating a rotating core catcher which tends to disintegrate and grind up highly fractured cores.
A still further object of the present invention is the provision of improved coring apparatus in which a core sleeve positioned between the inner barrel in the intermediate tube is maintained in compression by a weight and wherein the intermediate tube is connected to a nonrotating inner barrel. The intermediate tube includes a member which extends upwardly into the bottom of the inner barrel, but is spaced therefrom to permit movement of the core sleeve and catcher forming segments. As a result, the space between the lower end of the inner barrel and the core shoe is kept free of crushed and ground material.